1. Field of the Invention
The present invention relates to a linear driving device for a high-speed and high-precision motion.
2. Description of the Related Art
In recent machines and devices such as machining tools, measuring devices, etc., a linear driving device using a linear motor or a voice coil motor is widely used to meet requirements of high speed and high-precision. This linear driving device comprises a slider as a movable member and a base as a stationary member. When the slider as the movable member is accelerated, a reactive force of the acceleration force is exerted on the base in a direction opposite to the direction of acceleration of the slider. In performing a high-speed motion of the linear driving device, a large acceleration can be produced for the high-speed motion by simply increasing a driving power, but the reactive force exerted on the base increases with the increase of the acceleration of the slider. In the machine requiring a precise motion, a temporary distortion or inclination of the machine influenced by the reactive force is not negligible even if it is of a slight amount. It is possible to reduce the influence of the reactive force by enhancing rigidity of the machine, but the machine is made large and heavy. If the slider is designed to be small and light in order to reduce the reactive force, a purpose of the linear driving device is restricted. Further, in the case where the slider is driven to reciprocate at high speed, the slider functions as a vibrator to vibrate the linear driving device, so that a damping device for reducing the vibration is needed. In this case, the vibration caused by the slider reciprocating at a constant cycle can be reduced by a simple damping device. However, it is necessary to drive the slider to reciprocate at different cycles for different purposes of the device, so that an active control of the damping device is needed, to make the device complicated and costly. Anyway, since it is not possible for these techniques to completely eliminate the reactive force and thus the vibration, it is hardly possible not to transmit the vibration to members outside of the linear driving device. Thus, it is desirable to realize a linear driving device capable of canceling the reactive force and thus the vibration within the linear driving device.
There have been proposed a linear driving device having a function of canceling the reactive force using two sliders to move in opposite directions so as to cancel the reactive force with the driving force. In this linear driving device, however, only one of the two sliders is used for driving an object and the other of the sliders is not used for driving an object since a purpose of the linear driving device for machining or measurement using both of the sliders is greatly restricted. Further, a size of the linear driving device is rendered substantially twice as large as the conventional linear driving device and thus it is difficult to make the device compact.
An object of the present invention is to provide a compact linear driving device capable of fundamentally canceling a reactive force produced in acceleration and deceleration of a slider within the linear driving device.
A linear driving device of the present invention comprises: a base; a driving member supported movably with respect to the base in opposite linear directions on the base; and a slider driven by the driving member and supported movably with respect to the driving member in the same opposite linear directions as the driving member. With this arrangement, a driving force and a reactive force thereof in acceleration and deceleration of the slider are canceled in pair within the linear driving device and no influence of these forces is exerted outside of the device.
The driving member may be supported on the base means of a hydraulic bearing, so that substantially no force is transmitted to the base. In this case, an exciting coil of the driving member may be coated with a resin layer so that a surface of the resin layer constitutes a bearing surface of the hydraulic bearing.
Further, the slider may be supported on the driving member by means of a hydraulic bearing. In this case also, an exciting coil of said driving member is coated with a resin layer so that a surface of the resin layer constitutes a bearing surface of the hydraulic bearing.
The driving member and the slider may have different weights, so that they have different strokes of motion.
Weight distributions of the driving member and the slider may be set symmetrical with respect to an axis of motion of these members, so that any moment of rotating these elements is not produced in driving the slider.
Power cables for supplying an electric power to the driving member may be arranged between the base and the driving member to function as a spring for applying elastic force to the driving member in the direction of linear motion thereof, so as to eliminate deviation of positional relationship in linear motion of the driving member with respect to the base.
The driving member and the slider may constitute a linear motor.